The preamble of claim 1 considers the state of the art known from DE 44 17 569 A1 which describes a closure for a container that holds a free-flowing product. This closure has a fixed lower part, which can be closely fastened to a container neck and a cover with an externally protruding connecting piece, whereby a displaceable upper part is coaxially displaceable on the lower part between an outer position and an inner position. Except during ventilation, the upper edge of a beaker-shaped diaphragm valve consisting of a flexible elastic material seals the underside of the upper part, and said valve has perforations in its base, which are closed in the resting position of the upper part, and continuously pretensions the upper part in the direction of its outer position. When pressure is exerted on the container, a side room of the closure can be filled with the pressurized product. As a result, the upper edge of the valve is sealingly pressed against the upper part and the valve is bent outwards by pressure onto its side walls through an extraction opening and is opened for the release of the product.
CH 275 750 describes a container with a device for delivery of limited amount of a fluid, wherein the device is provided with a closing means consisting of a elastic flexible material which comprises at least one through hole automatically closing due to the effect of elasticity. A pressure piece is provided for deforming the closing means for reducing the volume of the container und for being adapted to open the through hole for discharging fluid. The closing means is provided as a diaphragm, while the pressure piece is axially displaceable in front of the diaphragm so that by means of displacement of the pressure piece the diaphragm can be bent to the inside of the container. This, the through hole is opened and at the same time the volume of the inside of the container is reduced so that a certain amount of fluid is extruded to the through hole.
With closures for containers that hold a free-flowing product, the metering of the amount of the free-flowing product that is to be released in dependence on its viscosity is often difficult because the fine-tuning of the displaceable upper part of such a closure is often not only cumbersome and difficult to handle but also time-consuming. Furthermore, to fulfill the purpose of fine-tuning, the constructive effort for such closures is often economically disproportionate.